Upon update user sees:

Beginning migration of archive.ar_user and archive.ar_user_text to archive.ar_actor
User name "Move page script" is usable, cannot create an anonymous actor for it. Run maintenance/cleanupUsersWithNoId.php to fix this situation.

User name "Delete page script" is usable, cannot create an anonymous actor for it. Run maintenance/cleanupUsersWithNoId.php to fix this situation.

$ php cleanupUsersWithNoId.php
Param prefix required!

https://www.mediawiki.org/wiki/Manual:CleanupUsersWithNoId.php says

cleanupUsersWithNoId.php is a maintenance script that cleans up tables that have valid usernames with no user ID. It should
once be run in wikis that contain imported revisions or global blocks via the CentralAuth extension.

The user never imported revisions nor used such extensions.

So he should not be asked to run some script.

update.php should notice Move page script and Delete page script
entries and deal with it itself without telling the user to run some
script.

Or at least tell the user what "prefix" you want him to use.

P.S., --prefix should not be within [ ] on the --help output as it is
not optional.

P.S.S., After cleanupUsersWithNoId.php the need of an additional run of
update.php needs to be mentioned. (This second run of update.php will say:)

Migrating actors to the 'actor' table, printing progress markers. For large
databases, you may want to hit Ctrl-C and do this manually with
maintenance/migrateActors.php.
Creating actor entries for all registered users
... 1 - 101
... 102 - 202
... 203 - 303
... 304 - 372
Completed actor creation, added 0 new actor(s)
Beginning migration of revision.rev_user and revision.rev_user_text to revision_actor_temp.revactor_actor
... rev_id=3219
Completed migration, updated 1 row(s) with 1 new actor(s), 0 error(s)
Beginning migration of archive.ar_user and archive.ar_user_text to archive.ar_actor
... ar_id=87